Tree of the month: November 2022 - English Oak

Each month we will be featuring a species of tree found on Parkwood Springs. Visit our tree of the month page for further details here.

There are two native oaks that we will be highlighting this month, Pedunculate and Sessile Oak.

English oak can live for hundreds of years and support an incredible 2,300 species of wildlife, including birds, bees, wasps, butterflies, and mammals.

English oaks is dense, water resistant, high in tannins and doesn’t warp for centuries. It has been used for buildings, bridges, sea defences, and furniture. The Vikings used it to make their ships, as did the Royal Navy into the 19th century.

Young great tits and blue tits rely on the tortrix moth caterpillars that live on oaks. Bats and birds live in the holes in the trees. Mice, squirrels, badgers, deer, and jays eat their acorns (but they are toxic to dogs). English oak acorns are on stalks (‘Pedunculate’) and the leaves are stalkless. This is opposite to our other native oak, on Parkwood Springs - the Sessile oak.

Mast years. The amount of fruits and seeds on some plants and bushes can vary enormously from year to year. Some of this is down to weather but it is likely to be more interesting than that. A heavy crop on trees like Oak and Beech is called a ‘mast year’ and occurs every few years. Producing a lot of seeds uses a great deal of energy and reduces the amount the tree can grow that year. It is thought that the trees have evolved to maximise seed production some years, to ensure new seedlings germinate and the species spreads, while producing less other years, so maximising the energy put into the existing tree’s growth and strength whilst also limiting the populations of their predators. For the Oak, Jays, mice and Squirrels are among the main common species that feed on the Acorns. There is much we still have to find out about the subtle evolutionary strategies of even our best known species.

Some Oak Facts

• The oldest known Oak in the UK is about 1,000 years old.
  
• They are thought to have first appeared around 65 million years ago.
  
• An average Oak will produce around 10 million acorns in its lifetime.
  
• They have to be around 20 years old before they produce acorns and 150 before the wood is really useful.
  
• Drought stress is one of the key factors contributing to Acute Oak Decline disease.
  

Some Oak Myths and Legends

• From the Greeks to the Celts, many civilisations have held the Oak to be a sacred tree.
  
• The most powerful Gods were associated with Oaks, from Zeus and Jupiter to Thor.
  
• Druids practiced sacred rites under the Oak, and the association with thunderstorms may have been linked to the fact that Oak trunks are sometimes split by lightning strikes.
  
• Many settlements had ‘Gospel Oaks’ on their boundaries- trees where the Gospel would be read during the annual ‘beating of the bounds’ ceremonies.
  
• Oak Apple Day, 29th May, was celebrated into the 20th Century to commemorate King Charles II, who was said to have hidden from the Roundheads in an Oak tree
  

Oak Galls
There are about 50 tiny wasps whose eggs and larvae create galls (abnormal growths) on our native Oaks. The wasps are non-stinging and mostly tiny, looking more like flies. Here are some of the most common:

Marble Gall

• These galls were imported in their thousands before being introduced to our trees from the Middle East in the 19th Century.
• High in tannins, they were crushed and mixed with ferrous sulphate to create a valuable, long-lasting ink and dye, from the 5th to the 19th Century. They were also used in tanning. These are common on English Oak.
• By late summer you can see the hole from which the wasp, Andricus Kollari, has emerged.

Knopper Gall
These didn’t arrive in the UK until the 1950’s but have spread rapidly, mostly on English Oak. The eggs are laid on the freshly pollinated flowers causing them to mutate as the acorn develops. The gall falls in autumn when the adult wasp emerges.

Oak Apple Gall

• This gall appears on English and Sessile Oak.
  
• The tiny wasp, Biorhiza Pallida, lays several eggs inside the dormant leaf bud.
  
• They hatch in spring and start to form the ‘apple’ gall, maturing in summer, when they eat their way out of the gall.
  

Spangle Gall
There are 4 common types of spangle gall, laid on the underside of English and Sessile Oak leaves. The wasps emerge in summer.

Sessile Oak

Many of the oak trees on Parkwood Springs are Sessile Oak. Sessile oaks differ from English oak in two key ways. Sessile means ‘stalkless’ and refers to their stalkless acorns. The other main difference is that the leaf-stalks are longer than on English oak- see drawing.

Squirrels, jays and badgers love their acorns, and many species of caterpillars feed on their leaves, including the oak tortrix caterpillars which provide the main food for young blue and great tits. 326 species of wildlife have been found only on oak trees. Fungi grow on their bark, and many birds and some mammals nest and roost in them.

Sessile oaks are more common in the less fertile, thinner soils of north and west Britain. Many were felled and their charcoal used for early iron-smelting. The timber was also used to make barrels and casks. The oak bark was used in the past for the local tanning industry at Oxspring Bank on Parkwood Springs. Remnants of once more widespread ancient woodland remain in Scraith Wood near Herries Rd.